Make use of a logging implementation or facade

[CodeDead]

Currently, errors are printed to the console, but perhaps it would be better to utilize a logging facade like SLF4J ?

[mkpaz]

Yes, it's in the backlog. Since there are no third-party libs, JUL should probably be enough. In normal mode, there's already exception dialog. I doubt that someone who just wants to see a quick feature preview need more than this. But log can be used in dev mode to print CSS errors when debugging a custom CSS theme.